Two agents drove through the scene of an investigation of a suspicious package outside White House in March

WASHINGTON—Two senior Secret Service agents were “more likely than not” impaired by alcohol when they drove through the scene of an investigation of a suspicious package outside the White House in March, according to a report released Thursday.

The report by the Department of Homeland Security’s inspector general is the first official account of an incident that prompted renewed scrutiny of the Secret Service. The agency already had...